Obesity is one of the most pressing public health problems in the United States. Through its negative influence on cardiovascular disease, diabetes, and cancer, obesity is a significant contributor to premature morbidity and mortality, as well as economic costs. Despite the magnitude of the problem, the public health system is faced with an almost complete dearth of population-level solutions to encourage sustained weight loss or halt weight gain. A large contributor to recent rises in obesity is that highly caloric foods are increasingly eaten outside the home, particularly fast foods. As such, one recently proposed population-level solution is a policy dictating mandatory calorie labeling of all menu items in fast-food restaurants. However, these policies are currently playing out across the country with little to no evidence as to their potential effectives in altering food choice. This project proposes to study calorie labeling as it plays out in two cities to provide evidence as to its effectiveness in combating obesity. The introduction of calorie labeling in some cities and not others provides us with a unique opportunity to study a natural experiment. We will utilize a difference-in-difference design to study calorie labeling as it is introduced in two cities but not in two, separate control cities. We will collect data before and after labeling is introduced in each city (intervention and control) via two separate means. To objectively measure the caloric content of food choice and satisfy our primary aim, we collect receipts from randomly sampled fast food restaurants in the intervention and control city. For our secondary aim, to provide greater insight as to the effectiveness of labeling as well as why labeling is effective or not, we will conduct a telephone survey at the same time the receipt collection occurs. We will focus our examination on the decision making of the consumer, utilizing the concepts of behavioral economics. Even though calorie labeling is being considered and implemented across the country, we have little to no knowledge as to its potential effectiveness. This project has the potential to provide significant insight as to whether this policy is indeed effective in combating the obesity epidemic. Moreover, it will shed light on why the policy is effective or not. The long term goal is to build on this knowledge to develop effective public polices to combat obesity.